Conventionally, a hybrid electric vehicle that has an engine and an electric motor as the drive section comprises two types of battery, namely a high voltage battery for driving the electric motor, and an auxiliary low voltage battery for lamps and audio systems and the like. The batteries installed in the vehicle are constructed so that, taking maintenance into consideration, the batteries are charged by a motor generator installed in the vehicle.
The construction of a conventional hybrid electric vehicle is shown in FIG. 16. The reference numeral 8 indicates an engine and the reference numeral 9 indicates an electric motor, and power is transmitted from the engine or the electric motor, or from both the engine and the electric motor, to the tires via a power switching mechanism 10. The electric motor 9 is controlled from a high voltage battery 70, via a power conversion device 30. The reference numeral 80 indicates an alternator, in a system configuration in which a low voltage battery 90 is charged by the rotation of the engine. The charging of the high voltage battery employs a setup in which the electric motor 9 operates as a generator, and charges the high voltage battery 70 via the power conversion device 30.
Furthermore, FIG. 17 is a structural diagram showing another conventional hybrid electric vehicle. The point of difference from the construction in FIG. 16 is that instead of being charged using the alternator 80, the low voltage battery 90 is charged from the high voltage battery 70 via a DC—DC converter 100 (see “TOYOTA ESTIMA HYBRID new vehicle manual, product number 61994”, Toyota Motor Corporation Service Division, published June 2001, p 0-9, p 1-31).
Moreover, regarding the motor generator, many motor generators with field winding systems have been proposed, including known motor generators which comprise two windings, namely a winding connected to the high voltage battery, and a winding connected to the low voltage battery (see Japanese Patent Laid-Open Publication No. Hei 6-105512, pages 1 and 3, FIG. 1).
In a conventional electric vehicle drive system such as those described above, it is necessary to either provide two types of motor generator, for the main high voltage system and for the auxiliary low voltage system, or to provide one type of motor generator and a separate DC—DC converter. Accordingly, problems arise in that more mounting space is required, and in that the associated costs increase.
If the motor generator is configured with a two winding field winding system, a problem occurs in that when winding the windings that are to provide power for the vehicle, the physical size of the motor generator becomes extremely large, and it cannot be installed in a vehicle. In addition, another problem arises in that because a field winding system is used, it is difficult to control the respective windings at the same time.
Accordingly, an object of the present invention is to provide a compact and low cost electric vehicle drive system using a magnetic field system which integrates two types of motor generator.